Method of making laminated paper



Patented Jail.

PATENT OFFICE D 1,986,951 nmrnon or name mmm'rn mesa Lloyd L. DodgeBhinelander, Wis., Bhinelander Paper Company,

assignor to Rhinelander,

Wis, a corporation of Wisconsin No Drawins.

Application December 6, 1933,

Serial No. 701,155 8 Claims. (Cl. 154-40) This invention relates to amethod of making laminated paper and more particularly to a method ofmaking a highly calendered, relatively transparent laminated sheetofpaper, although my '5 invention is applicable generally to themanufacture of any type of laminated paper which requires a calenderingstep in its preparation.

It has heretofore been customary in the manufacture of laminated paperof a highly calendered type to calender the individual sheets of paperseparately and then combine the finished sheets on suitable laminatingequipment. In accordance with such prior practice, therefore, therewould be as many calendering operations as there were number of plies inthe final laminated sheet. This procedure involves numerousdisadvantages in the way of attendant higher cost of manufacture andinferior quality of product.

Inthe calendering of paper, especially in the lossbecause of breakage ofthe sheet in passing through the calender stack. Also, where theadhesive used in laminating is applied to the surface of a calenderedsheet,poorer adhesion is obtained becauseof the tendency of the adhesiveto lie on the surface of the polished, dense sheet rather than topenetrate into and become anchored in the sheet..

Furthermore, where the individual plies of paarately calendered prior tothe laminating operation, the cost of calendering is directlyproportional to the number of plies in the final laminated product.

According to my present invention, the individual plies of paper are notseparately calendered but are first combined into a laminated sheet andthe laminated sheet then calendered to produce the finished product.This tends to reduce the breakage on the calender stack and eliminatesone or more calendering operations depending upon the number of plies inthe laminated product. Further, the combining of the constituent pliesunder the pressures and at the temperatures attained in the calenderingoperation results in a greatly improved bond between the plies of thelaminated sheet. In fact, the bond is of such strength that theindividual plies cannot there'- after he separatedintact except by theapplication of sumcient heat to soften or melt the binding agent. I

a My invention con 'plates either combining the constituent plies on.any suitable type of laminating machine prior to the calenderingoperation, or else combining the plies right at the case of light weightpaper, there is a considerable per making up the final laminatedsheetare sep calender stack. In the latter method, one or more of theconstituent plies is coated with a suitable adhesive, cement orthe likeand the temperature and pressures of the calender stack relied upon tobond a second ply to the coated surface 5 ,Of the first ply.

It is'therefore an object of this invention to provide a method ofpreparing laminated paper in accordance with which the cost ofcalendering ed product considerably improved.

It is a further important object of this invention to provide amethod ofmaking a highly calendered, relatively transparent, laminated paper,wherein the constituent plies are combined either 15 ahead of or at thecalender stack and the calen dering operation is relied upon to bond theplies firmly together and at the same time finish the sheet.

Other and further important objects of this invention will becomeapparent from the following description and appended claims.

The paper that is to be used in preparing a laminated product embodyingmy invention may be any type of paper that requires a calenderingoperation in the course of its manufacture into a laminated product.More specifically, however, my invention contemplates the use ofcomparatively well hydrated stock, such as is used in the. manufactureof sulphite, greaseproof, glassine 30 and parchmentized paper. Thesetypes of paper are largely used in the manufacture of laminated papersfor the reason that they are relatively transparent after supercalendering and possess. desirable properties of flexibility andstrength that adapt them for wrapping purposes. In order to increase thesoftness and flexibility of papers of this. character, they may beplasticized in the course of their manufacture in accordance with themethod disclosed in my copending application entitled Method 'of andapparatus for treating paper, Serial No. 647,953, filed December 19,1932, and my copending application entitled Paper and method of f makingsame, Serial No. 698,075, filedNovember 15, 1933.

Various weights of paper may be used in making my laminated product,but, in general, it is "customary to use the lighter weights, such asthose ranging between 15 lbs. and- 35 lbs. per. ream. According tooneembodiment of myinvention, the paper is finished on the paper machine,which may be of the Fourdrinier, cylinder or Yankee Eourdrinier type.and is then coated on one ,side with a suitable adhesive. The adhesivemay be any of the known types commonly used is greatly reduced and thequalityof the laminat- 1o in making laminated paper, such as theso-called cements, hot melt adhesive or the glue type of adhesive. Thecements include solutions of a bonding agent in a volatile organicsolvent, of which rubber dissolved in benzene and cellulose nitrate andresins or gums dissolved in lacquer solvents are typical examples. Iprefer to use the latter type of cement since it gives a moresatisfactory and more permanent bond and imparts moistureproofproperties to the laminated sheet.

After the sheet has been coated with a cement, or other adhesive, it isrun through the usual type of laminating equipment to combine it withanother sheet of similar or different character, but uncoated. In thelaminating operation, the superimposed plies are subjected to only alight pressure and to a temperature sumcient to effect the bonding ofthe sheet. Where a three ply sheet is to be made, one sheet may becoated on both of its sides with a cement and then run between other,uncoated sheets, one on each side, through the laminating machine.

Where the sheets are to be treated prior to the final calenderingoperation, I prefer to combine the individual plies as just described.The laminated sheet is then subjected to the desired treatment beforepassing it through the supercalenders. As an example of a suitable typeof treatment, the laminated paper may be subjected to a moisteningoperation, using eitherplain water or water having dissolved therein asuitable plasticizing agent, such as glycerine, a hygroscopic sugar likeglucose or dextrose, or combinations of hygroscopic liquids and solids.The paper is preferably moistened until it contains between 10 and 40%of water, usually around 25%, and after the paper has stood in the formof a roll until the moisture has uniformly penetrated throughout themass, the paper is then passed through the supercalenders.

supercalenders having steam preferably employed, since this type ofsupercalender imparts a higher finish and greater transparency to thesheet than would supercalenders of the book paper type. As is wellknown,

glassine supercalenders are built up with alter-- nate compressed fiberand steam heated chilled steel or iron rolls. These rolls are maintainedunder heavy pressure and are heated to raise the temperature of thecement or other bonding agent above its softening point and cause thebonding agent to be thoroughly impregnated into and anchored in thefibers of the constituent plies of paper as the laminated paper ispassed through the calender stack.

In another embodiment of my invention, the constituentplies arenotsubjected to a laminating operation ahead of the supercalenders but thelaminating is'carried out directly upon the supercalender stack. Asbefore, one or more of the constituent plies is coated with a heatsealing or thermoplastic cement, adhesive or the like and another ply,or plies, of uncoated paper is led into the calender stack insuperimposed relation to the coated ply. The pressure and temperature ofthe calender stack are s'umcient to effect the bonding of theconstituent plies and thus form the laminated product. directly on thesupercalender stack.

It is thus apparent that my invention contemplates the carrying out ofthe bonding and-finishing operation simultaneously on a calender stack,rather than employing separate calendering steps for each constituentply and a separate laminatheated rolls are ing operation. One of thegreat advantages of my method is that the sheet passes through thesupercalender stack as a multiple sheet composed laminated product onthe same weight basis than laminated papers made in accordance withheretofore known methods.

By the use of certain types of cements and adhesives, the properties ofthe laminated product may be greatly improved, as to its transparency,and its resistance to the penetration of moisture, water, grease andgases. For this reason, I prefer to use a cement of the thermoplastictype such as may be prepared by the use of nitrocellulose, resins, gumsand waxes in accordance with well known practice. A cement that isparticularly suited for my purposes is described in the Roy W. SextonPatent No. 1,926,918. A cement of this character forms, upon evaporationof the organic solvent, a thermoplastic coating that is non-tacky at lowor ordinary room temperatures but which exhibits excellent bondingproperties when heat and pressure are applied. Where the sheets are tobe laminated before being passed through the supercalenders, sufilcientheat and pressure is used to effect a fairly good bond between theconstituent plies so that the sheets may thereafter be handled as asingle sheet and be' subjected to any desired treatment, as, forinstance, the treatment with moistening and plasticizing agents as abovedescribed.

The use of my method of laminating paper greatly reduces the amount ofcement, or ad-' hesive, required to effect a satisfactory bond, due tothe greatly more efiicient bonding action that can be obtained onsupercalenders than is possible on the usual type of laminating machine.As little as two pounds of solid bonding agent per ream of paper may beused in my process, where for substantially equivalent bonding strength,almost twice as much solid bonding agent per ream of paper would berequired in the usual laminating process.

Where particularly improved resistance to the penetration of moistureand water is not required in the finished laminated product, varioustypes of adhesives, such as glue, casein, silicates and the like may beemployed. It is also possible to employ hot melt adhesives, which aregenerally mixtures of resins, gums and waxes and which are used withoutvolatile solvents. The hot melt type of adhesive is applied in a heated,molten condition to the surface of one of the plies and another plycombined therewith while the adhesive is in that condition.

It will be understood that although my invention has been describedchiefly in connection with the manufacture of laminated glassine paperand other papers of that general character, my process is applicable tothe manufacture of any type of laminated paper or fibrous material inthe course of which the paper or fibrous material is tobc heavilycalendered, or. may advantageously be heavily calendered. By the term"heavy calendering is meant the subjecting of paper or other fibrousmaterial to a rolling and smoothing operation at pressures in excess of1,000 lbs. per sq. m. p

I am aware that numerous details of the process may be varied through awide range without departing from the principles of this invention, andI, therefore, do not purpose limiting the patent granted hereonotherwise than necessitated by the prior art.

I claim as my invention:

1. The method of forming laminated glassine paper, which comprisesadhesively securing together a plurality of plies of uncalenderedgreaseproof paper in superimposed relation with a thermoplastic bondingagent and subjecting the plied material to a supercalendering operationat an elevated temperature to thoroughly bond the plies together andsimultaneously finish their outside surfaces. 1

The method of making laminatedglassine paper, which comprises coating aweb of uncalendered grease-proof paper on one side thereof withabondingagent having resistance to the penetration of water and moisture,imposing another web of uncalendered grease-proof paper on the coatedside of the first web, and calendering the two webs together to bondtheir inside surfaces and finish their outside surfaces.

3. .The method of making relatively transparent laminated paper, whichcomprises interposing a layer of thermoplastic cement between plies ofdried uncalendered well hydrated paper, incorporating between 10% and byweight of water into said pliedpaper, and finally subjecting said pliesto heavy calendering pressure at an elevated temperature to create afirm bond between the plies and to finish their outside surfaces.

4. The method of making laminated glassine paper, which comprisesinterposing a layer of thermoplastic cement between superimposed pliesof uncalendered grease-proof paper, incorporating between 10% and 40% byweight of water into *said plied paper, and finally subjecting saidplies gether by a thermoplastic cement, the outside surfaces of saidlaminated paper being highly calendered.

7. Atransparent and flexible laminated glassine paper composed ofconstituent plies of greaseproof paper having uncalendered surfacesjoined together by a bonding agent having good resistance to thepenetration of water and moisture, the exposed surfaces of said pliesbeing highly calendered to impart a smooth finish to the laminatedsheet. I

8. The method of making relatively transparent laminated paper, whichcomprises joining together by means of an adhesive a plurality of pliesof well hydrated light weight paper and subjecting the plied material ina moistened condition toheat, pressure and friction on a glassine typesupercalender to simultaneously bond theplies together and finish theiroutside surfaces;

LLOYD L. DODGE.

